1968 Z28 production code VIN stamp pad

[florissant]

The production code and VIN as stamped on the "pad" are interchanged top and bottom (left to right on a printed page) on my 302 engine. They are stamped on what I believe to be an original "as cast" surface (from my 35 year experience as a machinist/mechanical engineer). All the fonts seem to be of the correct size and style as in published photos in standard references. Anyone seen this before?

 

[motormonkey]

According to the Camaro Research Group, the stamping numbers on small blocks typically appear with the partial vin first(left side, if reading left to right) and the engine code application and assembly date to the right of it. However this wouldn't be uncommon to be found in the reverse order as big blocks have this typically. Without a photo to reference I couldn't tell if the letters/numbers you describe are "correct" or not. All I can tell you is a typical 302 code would read something like this; "F10I0MO" Which means Flint engine, Oct. 10th, 1967(since a 68 date would be for a 69 and this code would be different). Hope this helps

 

[florissant]

Thanks motormonkey---the production code on my Z28 reads: VO327MO. This decodes as V=Flint Plant March 27 The suffix MO signifies a 302. All the fonts are identical in their detailed style to photos that I've seen in pictures of 302 blocks. In his interesting articles, John Hinckley indicates that these stampings were "hand-hit" using a small "gang-die" and sledge hammer! The guy doing this must have been a mean S.O.B.; considering that hundreds of these stampings (maybe thousands) needed to be made on a moving production line. Basically, as I said, everything seems "normal" (textbook), except that the VIN and Production Code groups are transposed top-to-bottom on the stamp pad. I'm just trying to verify if this can be a genuine variation, relative to "textbook". Considering that this stuff was hand done; it seems that errors would likely occur that would not be recorded in a standard reference book (MacNeish). In all other respects, my engine seems normal--casting numbers, casting dates, etc. Also, my car is a "matching-numbers" one. Sure would like more input guys. As everyone knows, real Z28's with real 302's are scarce!

 

[motormonkey]

I would believe that errors are more likely than exception. I respect Mr. MacNeish's work in reference and as in car for car(or motor to motor) checking but in 1968 they only made a few thousand of these engines. Unlike 1969 models where there were over 20,000 engines produced just for production alone. I have also read where these codes were hand stamped. Usually the stamps were arranged in a block of up to 7 characters and they were then set to a specific location on the block pad. However in instances these code blocks were disoriented from normal on occasion. You could always call MacNeish for further info after explaining what you have, but I hear that he doesn't give out info unless you have him certify your car. Bare in mind there are other sources for his specialties which may not be so restricted. I hope I have helped you in some way.

 

[florissant]

Thanks motormonkey, Interesting conversation here. The analog nature of code stamping seems incredible today! Especially since production might be 5000 engines per day. The "stamper person" was required to select correct gang stamps from a rack next to him for each engine application (suffix code). at a rate of approx. 30 seconds as the "line" moved along. Quite a task with a "sledge hammer"; and when engine types arrived in a completely random manner. Many errors must have occurred.---From Johe Hickley' paper. Cheers

 

[motormonkey]

Exactly! It is amazing to me how these guys pulled it off. I would further submit that errors most likely occurred during shift changes as information often got lost or misplaced around these times. Allen Colvin states in his book ; "The engine code characters were in general fitted into a metal holder and locked by a Allen key. The holder was then placed over the block pad and gang stamped with a dead blow hammer. All 65-69 code characters were 3/16" high". There is also some mention of block code/vin code orientations changing, mostly on big blocks because the gang stamps wouldn't clear the cylinder head core cap screws on the ends of the head so the letters were askew on the pad. They began changing the orientation from VIN on left, build date/application code on right to vice versa but he says it was unclear when this took place and how many engines were effected. He says 1965 on big blocks and possibly all others is a good bet, since that is when the Mark IV went into production. I have only seen left hand VINs on my engines but I also haven't checked every last one so this doesn't mean much. He also states the vin codes weren't always stamped on engines until 1960 on Corvettes and around 1962 for 327s and 409s, possibly others. My old 62' 283 block has a vin stamp. In 1968 it became across the board on all Chevy engines as a theft deterrent. I hope this last bit helps ease any doubts.